Tag | (0018,1150) |
---|---|
Type | Optional (3) |
Keyword | ExposureTime |
Value Multiplicity | 1 |
Value Representation | Integer String (IS) |
Example Values |
|
Time of X-Ray exposure in msec.
If Acquisition Type (0018,9302) equals SPIRAL, the value of this Attribute shall be Revolution Time (0018,9305) divided by the Spiral Pitch Factor (0018,9311). See Section C.8.15.3.8.1 and Section C.8.15.3.2.1.
Shall not be present if the corresponding Attribute, Exposure Time in ms (0018,9328), is present in Multi-energy CT Acquisition Sequence (0018,9362) and the value of this Attribute is not the same in all Items of the Multi-energy CT Acquisition Sequence (0018,9362).
An example of how the value of Exposure Time in ms (0018,9328) can be calculated:
The Exposure Time Texposuretime of a volume shall be the time of the X-Ray radiation in position with this volume. It depends on the travel speed and the total collimation width.
Texposuretime of the volume represented by a distinguished frame of a Spiral Scan can be calculated as follows:
Texposuretime = N x S / Vtravelspeed
CTpitchfactor = DD / N x S
Vtravelspeed = DD / Trevolutiontime
From this the exposure time can be derived:
Texposuretime = N x S x Trevolutiontime / DD = Trevolutiontime / CTpitchfactor
Legend:
DD = Table Feed per Rotation (0018,9310) in mm distance moved by the patient support in the z direction per 360° revolution in Spiral scanning
S = collimation of a single slice in mm
N = number slices
N x S = Total Collimation Width (0018,9307) in mm
Vtravelspeed = Table Speed (0018,9309) in mm/second, travel speed of the patient table
Trevolutiontime = Revolution time (0018,9305) in seconds
CTpitchfactor = Spiral Pitch Factor (0018,9311)
Defined Terms:
identifies that the acquisition was performed by acquiring single or multi detector data while rotating the source about the gantry while the table is not moving; additional slices may be acquired by incrementing the table position and again rotating the source about the gantry while the table is not moving
identifies that the acquisition was performed by acquiring data while rotating the source about the gantry while continuously moving the table
identifies that the acquisition was performed by holding the source at a constant angle and moving the table to obtain a projection image (e.g., a localizer image)
identifies that the acquisition was performed by holding the table at a constant position and performing one or more acquisitions over time at the same location
identifies that the acquisition was performed while rotating the source about the gantry while the table movement is under direct control of a human operator or under the control of an analysis application (e.g., fluoroscopic image)